With recent technical improvements, we are able to culture canine urothelial cells in vitro with consistent success. We shall continue to work on improving the conditions of culture and characterizing the behavior of the cells as they become established in vitro. We are extending our studies to bladder epithelial cells from rabbit, swine, baboon, and man. When the normal behavior of these cell cultures has been adequately characterized, we shall treat them with chemicals believed to be carcinogenic in bladder or other tissues; and seek changes in cell behavior which may be indicators of "cell transformation" in vitro, and be related to neoplastic transformation in vivo. Such indicators may include changes in growth rate, cell morphology, intercellular relationships, karyotype, or changed culture condition requirements. With such biological markers of cell transformation identified, the system will be examined for the biochemical effects of the chemical treatment. We shall look for binding of the reagent to specific macromolecules, and shall concentrate our attention on effects on nucleic acids and on the enzymes associated with nucleic acid metabolism, such as changes in relative rates of synthesis or processing, strand breaks, or other alterations in structure or function. The various tissue culture systems will be evaluated for their usefulness in screening potential bladder carcinogens.